The present invention is related to force-sensing linkages and, in particular, to linkages used in aircraft control systems.
The prior art related to linkages used in aircraft control systems includes U.S. Pat. No. 6,311,566 to Ferguson. This patent shows the use of an inner first tube, a second outer tube, a spring connecting the first and second tubes, a position sensor connected between the first and second tubes and a stop assembly. Stop assembly limits the relative longitudinal movement between the first and second tubes to a selected range.
The stop assembly includes an eccentrically positioned, or off-center hole, formed in an inwardly directed flange on one tube. A stop nut attached to the other tube is inserted through the off-center hole. When the stop nut is then centered, lips on the stop nut limit the relative longitudinal movement of the flange to the distance between the lips.
Assembly of this linkage is awkward and cumbersome. In addition, only a relatively small crescent shaped portion of the stop nut engages the flange.
Another problem with this design is that friction forces between the tubes result in the generation of wear particles, contamination and inaccuracy of the force measurements provided by the sensor.
In addition, this design does not provide any limits on angular movement between the tubes, simply relying on the rod ends remaining coplanar because of the orientation of respective mounting points.